Introduction
Anomalies arising from the third and fourth branchial cleft remnants are quite rare. In particular, branchial abnormalities related to the pharynx are only a small subset of the already rare collection of branchial cleft lesions. Branchial abnormalities with a sinus tract connecting to the pharynx usually present with acute suppurative thyroiditis and a thyroid abscess. The sinus tract connecting to the pharynx serves as a conduit for transmission of hypopharyngeal flora. Most cases of piriform sinus fistulas appear to have an inferiorly coursing branchial sinus with an aperture at the piriform sinus apex. They almost always present with a neck infection, frequently involving the left thyroid lobe. Therefore, anomalies thought to arise from the third and fourth branchial remnants do not seem to conform to the theoretic pathways of third or fourth arch fistulas. The discrepancy between the classical course of either third or fourth branchial anomalies and the observed course of infection related to the piriform sinus apex have led to alternative explanations related to the thymopharyngeal duct. The thymopharyngeal duct forms as the thymus descends during fetal development along a tract that more accurately accounts for the observed infection with thyroid involvement. Therefore, piriform sinus duct abnormalities are most likely secondary to an incompletely obliterated embryologic remnant of the thymopharyngeal duct (of the third branchial pouch). As such, the term “third branchial sinus” is likely most appropriate for branchial lesions with an aperture at the piriform apex and infection involving the thyroid gland ( Figs. 38.1 and 38.2 ).
Temporal Evolution: Overview
The typical presentation is that of recurrent infection and abscess formation in children. Of note, although branchial cleft abnormalities classically and most often present in children, they may also rarely present later in adulthood. The infection is adjacent to or involving the (predominantly left) thyroid gland. The left sided preponderance may be due to the asymmetric development of vascular components of the branchial arches. It is precisely the failure to recognize the underlying duct remnant that results in incomplete management and leads to repeated bouts of infection. Without recognition of the underlying abnormality, the initial sinus tract can be converted to an iatrogenic fistula as a result of nondefinitive incision and drainage procedures.
Branchial apparatus anomalies can present as cysts, sinuses, or fistulas. Because they frequently present with infection, when an inflammatory process or abscess is present between the piriform fossa and the thyroid bed in the lower left lower neck, particularly in a young patient, an infected piriform sinus fistula should be suspected ( Fig. 38.3 ). Once the inflammation subsides, a sinus tract can potentially be revealed on imaging. The presence of gas within a recurrent left-sided infected thyroid gland lesion is thought to be characteristic and highly suggestive of this entity in the pediatric population. The associated presence of air along the thymopharyngeal duct sinus tract is considered diagnostic. Imaging with oral contrast can help to delineate the underlying sinus tract, particularly once the acute inflammation has subsided. Suggesting the presence of an underlying branchial apparatus anomaly and performing the appropriate imaging to delineate the extent of the anomaly is important for surgical management because complete resection is crucial for minimizing the risk of recurrence. Pharyngoscopy reveals a sinus tract aperture at the apex of the piriform fossa. Definitive surgical management includes dissection of the sinus tract, as well as hemithyroidectomy. Because the recurrent laryngeal nerve is generally intimately associated with the sinus tract, care must be taken to preserve this structure.
